This invention relates to apparatus for cleaning liquids such as machine tool coolants which contain highly abrasive particles that usually are both ferrous and non-ferrous in nature so as to be both magnetic and non-magnetic. One such apparatus is disclosed in Marriott U.S. Pat. No. 3,456,797 and comprises the combination of a rotatable magnetic drum and a cyclone separator.
In such an arrangement, most of the magnetic particles in the dirty liquid are collected as swarf on the magnetic drum and the partially cleaned liquid then is delivered to the cyclone separator for final cleaning. As is well known, a cyclone separator produces a clean flow of liquid and also discharges a downward stream of dirty liquid--commonly called underflow--which contains particles separated from the liquid delivered to the cyclone.
In the apparatus disclosed in the Marriott patent, the dirty underflow of the cyclone is discharged onto the upper side of the magnetic drum so that the underflow may be strained through the swarf collected on the drum. In this way, the non-magnetic particles in the underflow are filtered by and captured in the collected swarf and thus the underflow itself is cleaned prior to being mixed with additional incoming dirty liquid flowing to the drum.